1. Field of the Invention
The present invention relates to a power controller of a drive circuit for driving a load.
2. Description of the Related Art
Recently, an over-current protection circuit which detects over-current flowing in a drive circuit (such as an inverter circuit) and a load to protect a circuit element of a drive circuit or the load from over-current is widely used in a load (such as a motor) driving device (for example, JP-H09-009672A).
Further, there is used a switching power supply which detects power consumed by a drive circuit and a load to allow constant over-power protection, rather than by limiting over-current flowing in the drive circuit and the load (for example, JP-2009-038854A).
Specifically, JP-H09-009672A discloses an overload protection device which is capable of protecting an electric motor from overload due to a momentary change of an armature current. The overload protection device carries out control to detect a current flowing in an electric motor 1 and makes an armature current to zero or limits the armature current below a limit value when a detected current signal exceeds a reference signal.
JP-2009-038854A discloses a low-cost control device (switching power supply) capable of suppressing torque pulsation of AC motor.
The overload protection device disclosed in JP-H09-009672A is effective to carry out over-current protection by limiting an input current. However, there is a problem that over-power protection cannot be carried out. On the other hand, the control device disclosed in JP-2009-038854A is capable of carrying out over-power protection and controls an over-current protection at a constant power, irrespective of a value of input voltage. Therefore, there is a concern that a large current would flow when voltage is low. Consequently, there is a problem that the circuit components are damaged by the large current and thus a malfunction may be caused.